The present invention relates to a method and apparatus for securing straight tubes between two tube sheets in a pressure-tight manner, especially in the manufacture of heat exchangers
German patent No. O24 56 811 -Krips dated June 10, 1976, belonging to the assignee of the present invention, discloses a method of securing straight tubes between two tube sheets In this heretofore known method, subsequent to a hydraulic expansion of the tube ends in the vicinity of the tube sheets, an additional rolling on of the tubes in the expanded region of at least one of the tube sheets is effected in order to produce a predetermined state of stress in the tubes that are disposed between the two tube sheets so that no overstressing of the tubes occurs in the later operating state.
With this known method, the state of stress in the individual tubes can be prescribed very precisely. However, the additional rolling-on process requires a considerable amount of time and effort.
It is an object of the present invention to simplify the heretofore known method and to produce a predetermined state of stress in the tubes that are secured between the two tube sheets in a single procedural step accompanied by securing of the tubes in the tube sheets.